عکس‌‌العمل جوامع گیاهی تحت چرا و قرق در شرایط ترسالی و خشکسالی کوتاه‌مدت (مطالعۀ موردی: اکوسیستم‌‌های نیمه‌‌بیابانی خراسان جنوبی)

چرای دام به‌همراه خشکسالی، به‌عنوان عوامل محرک کاهش تنوع زیستی در مراتع بر عملکرد اکوسیستم تاثیر می‌گذارند. با وجود این، عکس‌العمل اکوسیستم‌های خشک نسبت به دوره‌های مختلف خشکسالی اعم از کوتاه‌مدت، میان‌مدت و طولانی‌مدت متفاوت است. هدف از تحقیق حاضر، بررسی عکس‌‌العمل خصوصیات ساختاری جوامع گیاهی salsola richteri وzygophyllum eurypterum- artemisia sieberi در شرایط مختلف ترسالی و خشکسالی کوتاه‌مدت در دو مرتع تحت چرا و قرق در سال 1399 و 1400 در اکوسیستم‌‌های نیمه‌‌بیابانی خراسان جنوبی است. در این خصوص، درصد پوشش تاجی، تراکم و تولید گونه‌ها و شاخص‌های تنوع زیستی در داخل 120 پلات 4 و 16 متر‌مربعی مستقر در امتداد ترانسکت‌های 200 متری اندازه‌گیری شد. نتایج آزمون‌های ویلکاکسون و جایگشت نشان داد که خشکسالی کوتاه‌مدت باعث حذف گونه‌های یک‌ساله شد، اما تاثیر معنی‌داری بر درصد پوشش و تراکم گونه‌های چندساله نداشت (0/05≤p). در جامعۀ سالسولا، تنوع گونه‌ای در مرتع قرق سال نرمال (0/15=d-1) بیشتر از سال خشک (0/105=d-1) بود. در جامعۀ درمنه- قیچ تاثیر کاهش بارندگی بر تولید بیشتر از سایر خصوصیات پوشش گیاهی بود، در سال نرمال تولید کلیۀ گونه‌های گیاهی تقریباً صفر بود، به‌طوری‌‌که امکان اندازه‌گیری تولید، وجود نداشت. با در نظر گرفتن عکس‌العمل گونه‌های گیاهی به خشکسالی، گیاه ammodendron persicum در جامعۀ سالسولا به‌عنوان گیاه مقاوم به خشکی برای کاشت در طرح‌های احیای مناطق بیابانی توصیه می‌شود.

investigating the response of grazed and enclosed plant communities to short-term wet and drought conditions: a case study of south khorasan semi-desert ecosystems

introduction: considered two important contributing factors in reducing biodiversity in rangelands, drought, and grazing influence the performance of natural ecosystems. moreover, plant communities respond variously to drought periods under different management conditions. however, while many studies have so far been conducted on the response of plant communities to drought, it is not clear whether the ecosystems are more resistant or more vulnerable to drought. therefore, this study sought to examine the impact of grazing intensity (including lenient, moderate, and heavy grazing) on vegetation characteristics (such as canopy cover, forage production, and species diversity) of semi-desert ecosystems of south khorasan province under normal, wet, and drought conditions. material and methods: this study attempted to investigate the structural properties of salsola richteri and artemisia sieberi- zygophyllum eurypterum communities in the grazing and enclosed rangelands under short-term wet and drought conditions. to this end, canopy cover, density, forage production, and the richness and diversity of species were measured according to the guidelines set by the iranian national program for monitoring rangeland quality. moreover, the species abundance index was used to assess plant diversity indices. accordingly, after recording the plant density values and converting them to abundance ones, the species richness, dominance, diversity, and evenness were calculated using the adiv package. on the other hand, the standard precipitation index (spi) was used to assess the drought. finally, the statistical analysis of the data was performed using the wilcoxon signed-rank test and permutation test. results: the results of the spi analysis indicated that the salsola richteri community experienced normal and very dry years in 2019-2020 and 2020-2021, whose spi value was found to be 0.097 and 1.6, respectively. as for the artemisia sieberi- zygophyllum eurypterum community, the years 2019-2020 and 2020-2021 fell under relatively humid and normal classes, respectively, with their spi values being 1.14 and -0.70, respectively. moreover, it was found that annual species were eliminated by drought, especially salsola richteri and ammothamnus lehmanii which were affected the most among other species. accordingly, the production of salsola richteri was reduced from 800 kg/ha to 60 kg/ha and ammothamnus lehmanii was completely dried. however, the results showed that canopy cover and density of perennial species were not significantly influenced by drought (p≥0.05). for instance, ammodendrom persicum and stipagrostis pennata, which had the highest density in this region, were less affected by drought. on the other hand, in the enclosed rangeland, the species diversity of the salasola community was higher in the normal year (1-d = 0.15) than in the dry one (1-d = 0.105). it was also found that in the artemisia sieberi- zygophyllum eurypterum community, decreased precipitation rate was more influential in reducing forage production than other vegetation properties. in this regard, the production of all plant species was approximately zero in the normal year, with the grazing capacity being impossible to determine. discussions and conclusion: as found by the current study, drought exerted a significantly negative influence on the density, richness, and diversity of species in the salsola community, with species dominance being greater in the dry year than the normal one. therefore, it appears that compared to the artemisia sieberi- zygophyllum eurypterumcommunity, the salsola community enjoys a higher species diversity.